The invention relate to a surgical microscope with a stand, the microscope having altogether up to six degrees of freedom and being fixed on the microscope mounting by means of elements of the stand, the stand having two vertical pivoting axes, which are not subjected to any gravitational influence, and for the height adjustment a parallelogram linkage with weight compensation, which are formed in such a way that they can move smoothly and have arresting brakes.
In the case of such a stand (U.S. Pat. No. 5,213,293), the microscope can be brought into the desired position for the surgery with the aid of the stand. It has a weight compensation, so that it remains in this position even when articulating joints undergo slight braking. However, it is very laborious to accomplish this weight compensation. Subsequent adjustment of the microscope to change the image field must be performed manually.
In the case of another known microscope (U.S. Pat. No. 5,232,181), the adjustment about all the axes takes place in a motorized manner. For this purpose, only approximate weight compensation is required, which of course, is easier to accomplish than the fine compensation of the first-mentioned arrangement. The problem of this arrangement is that the setting of the microscope to a new assignment or new conditions by the motors takes place only very slowly, since fast automatic movements about the individual degrees of freedom would require motors that are too large and, in particular, are also dangerous. This nullifies the advantage that only approximate balancing is required.
For the manual handling of a surgical microscope on a stand, balancing is always required. It is not only weight compensation by counterweight, springs and pneumatic springs that is necessary, since the arms of the stand are of a certain weight, which is of course always the same. When adjustments are made to accessories of the microscope, which become necessary when performing operations, the center of gravity of the microscope shifts. Renewed weight compensation about the rotational axes then has to be performed. Taking into consideration the necessary rigidity of the microscope mounting, the mechanical complexity when there are a plurality of axes of rotation is considerable and, if it is wished to make weight compensation easier for the user, is further increased by motor drives. There are even known configurations (German Patent Nos. DE 4320443 A and DE 43 34 069 A) in which the weight compensation is carried out automatically on request by sensors, controllers and actuating elements.
The object of the invention is to provide a microscope with a stand with which the setting of the location of the microscope can be quickly performed manually, but a fine setting of the observable image field can be subsequently performed, without this handling being disturbed by gravitational forces or moments caused as a result of the latter.
Briefly stated, the invention in a preferred form involves the microscope being mounted on the stand by means of a third vertical axis, which is not subject to any gravitational influence. A first further axis is perpendicular to said third vertical axis and a second further axis is perpendicular to the first further axis. The further axes are designed such that they are essentially perpendicular to the optical axis of the microscope objective and can be adjusted by motor. The further axis that is closer to the microscope permits a lateral pivoting of the viewing direction (X direction) and the further axis that is arranged between the third vertical axis and the further axis that is closer to the microscope permits a pivoting of the viewing direction forward/backward or upward/downward (Y direction).
It is indeed known to free the mobility of surgical microscopes on supporting units by buttons on grips which are arranged on the microscope. When the buttons are actuated, electromotive brakes of the articulating joints of the stand are released. However, the invention is not confined to the capability of being able to perform the movements about these axes quickly by hand and then block the axes in this position. Rather, the invention also provides a combination of this manual adjusting capability with a motorized setting.
The relatively great adjusting distances of the stand are made available to the user/surgeon in a way known per se and a weight-compensated manner in the so-called xe2x80x9cfree floating mode.xe2x80x9d The user guides the device by a grip, for example with an integrated button, by which the movement can be enabled. At the same time, a fine weight compensation has been performed at the parallelogram arm. This overall weight compensation must be as accurate as possible, so that only very small forces are required for the settings. An imbalance at the two setting axes directly on the microscope does not present any problem if a motorized adjustment is provided for these axes and the motors are powerful enough to absorb the corresponding forces of the imbalance.
The rotations about the third vertical axis and the two further axes allow the surgeon to adapt the field of view to requirements. The special sequence of the two further axes at the same time provides a very expedient adjustability for different surgery conditions. This is because the optical axis of the surgical microscope is aligned completely differently in relation to the vertical for different surgical operations (for example, brain operations, spinal operations, and eye operations). If the sequence of the further axis is chosen to be different, this favorable alteration of the field of view is no longer possible.
The motor drives are expediently designed as servo drives. The set point input for these servo functions is performed in a preferred way by electrical force or moment sensors between the microscope and the operating element for the corresponding directions. The sensors are designed in such a way that they emit a signal which rises with the moment exerted by the user and occurring at the operating element about an axis and changes its algebraic sign when there is a change in direction. The operating elements are expediently adjustable, so that the user can adjust them into the position most comfortable for the user, without at the same time changing the position of the sensors in relation to the microscope, and consequently, the relationship between the signals and the effective direction.
In the case of longitudinal and transverse forces and in the case of moments perpendicular to the sensor axis, no signal is emitted. In a particularly expedient embodiment, the sensors are arranged in pairs in such a way that, when one sensor is relieved by a force exerted on the operating element by an operator, the other sensor is loaded. The two sensors are arranged on either side of a neutral line with respect to the moment to be detected or the force to be detected. The two sensors are under a pressure and are connected to each other in a bridge circuit, so that the signals produced by the pressure cancel each other out. If a moment or a force attempting to bring about a rotation about this line is introduced into the operating element, rising pressure occurs on one side of the neutral line, falling pressure on the other side. In a corresponding way, the bridge is unbalanced and supplies an output signal corresponding to the moment. Piezo elements, inductive sensors, capacitive pickups, resistive and optical force/displacement pickups may be used as sensors.
The signals are further processed in terms of control technology to perform the adjustments by means of motor drivers and servomotors. With adequate dynamics of the two servo controllers together with the free floating of the other four degrees of freedom, the setting times are reduced. While the user adjusts the microscope in the four degrees of freedom freed for movement, the moments introduced for setting the direction of the microscope axis act at the same time on the operating element and bring about the corresponding adjustment of the microscope with relatively great displacements and the servo adjustment of the small rotational movements does away with the effect known from purely servo systems that the user has to wait for a long time until the adjustment is completed.
The arrangement is expediently set up in such a way that the possible movements about the individual axes or degrees of freedom are limited to such an extent that the microscope cannot hit parts of the stand.